[SRU B/C: 1/2] virtio/s390: avoid race on vcdev->config

[Stefan Bader]

From: Halil Pasic <pasic at linux.ibm.com>

BugLink: https://bugs.launchpad.net/bugs/1788432

Currently we have a race on vcdev->config in virtio_ccw_get_config() and
in virtio_ccw_set_config().

This normally does not cause problems, as these are usually infrequent
operations. However, for some devices writing to/reading from the config
space can be triggered through sysfs attributes. For these, userspace can
force the race by increasing the frequency.

Signed-off-by: Halil Pasic <pasic at linux.ibm.com>
Cc: stable at vger.kernel.org
Message-Id: <20180925121309.58524-2-pasic at linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck at redhat.com>
Signed-off-by: Michael S. Tsirkin <mst at redhat.com>

(cherry picked from commit 2448a299ec416a80f699940a86f4a6d9a4f643b1)
Signed-off-by: Stefan Bader <stefan.bader at canonical.com>
---
 drivers/s390/virtio/virtio_ccw.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c
index 97b6f197f007..c94f38ef9a94 100644
--- a/drivers/s390/virtio/virtio_ccw.c
+++ b/drivers/s390/virtio/virtio_ccw.c
@@ -828,6 +828,7 @@ static void virtio_ccw_get_config(struct virtio_device *vdev,
 	int ret;
 	struct ccw1 *ccw;
 	void *config_area;
+	unsigned long flags;
 
 	ccw = kzalloc(sizeof(*ccw), GFP_DMA | GFP_KERNEL);
 	if (!ccw)
@@ -846,11 +847,13 @@ static void virtio_ccw_get_config(struct virtio_device *vdev,
 	if (ret)
 		goto out_free;
 
+	spin_lock_irqsave(&vcdev->lock, flags);
 	memcpy(vcdev->config, config_area, offset + len);
-	if (buf)
-		memcpy(buf, &vcdev->config[offset], len);
 	if (vcdev->config_ready < offset + len)
 		vcdev->config_ready = offset + len;
+	spin_unlock_irqrestore(&vcdev->lock, flags);
+	if (buf)
+		memcpy(buf, config_area + offset, len);
 
 out_free:
 	kfree(config_area);
@@ -864,6 +867,7 @@ static void virtio_ccw_set_config(struct virtio_device *vdev,
 	struct virtio_ccw_device *vcdev = to_vc_device(vdev);
 	struct ccw1 *ccw;
 	void *config_area;
+	unsigned long flags;
 
 	ccw = kzalloc(sizeof(*ccw), GFP_DMA | GFP_KERNEL);
 	if (!ccw)
@@ -876,9 +880,11 @@ static void virtio_ccw_set_config(struct virtio_device *vdev,
 	/* Make sure we don't overwrite fields. */
 	if (vcdev->config_ready < offset)
 		virtio_ccw_get_config(vdev, 0, NULL, offset);
+	spin_lock_irqsave(&vcdev->lock, flags);
 	memcpy(&vcdev->config[offset], buf, len);
 	/* Write the config area to the host. */
 	memcpy(config_area, vcdev->config, sizeof(vcdev->config));
+	spin_unlock_irqrestore(&vcdev->lock, flags);
 	ccw->cmd_code = CCW_CMD_WRITE_CONF;
 	ccw->flags = 0;
 	ccw->count = offset + len;
-- 
2.17.1